The present invention relates to the field of wireless communication. More particularly, it relates to the efficient use of the radio frequency spectrum by wireless communication devices.
Wireless communication networks are typically comprised of a mobile switching center, base stations and mobile/portable units (xe2x80x9cmobile unitsxe2x80x9d). The base stations are typically hardwired to the mobile switching center through communication lines such as optical communication lines. Each base station provides coverage for mobile units within a specified area called a xe2x80x9ccell.xe2x80x9d
When a mobile unit is within a particular cell and requests access, the base station for that cell assigns a frequency channel pair to the mobile unit. The frequency channel pair is comprised of an xe2x80x9cuplinkxe2x80x9d frequency channel, which is used for transmitting signals from the mobile unit to the base station, and a xe2x80x9cdownlinkxe2x80x9d frequency channel, which is used for receiving signals at the mobile unit from the base station. The frequency channel pair assigned to a particular mobile unit can be thought of as a single frequency channel and is often described as such by those skilled in the art. A mobile unit, such as a cellular telephone, can communicate with other mobile units or hardwired units, through its communications with a base station.
The use of mobile unit wireless communication devices such as cellular telephones, Personal Communications Networks (PCN), wireless Private Branch Exchanges (PBX""s), and wireless Local Area Networks (LANs) is rapidly increasing. However, the radio frequency spectrum, which is used in wireless communications, is essentially comprised of a finite number of frequency channels. Various channel allocation techniques have been employed for the efficient use of this limited resource.
Dynamic Channel Allocation (DCA) is a broad title for several techniques for efficiently using the radio frequency spectrum. In DCA techniques, channel pairs are not preassigned to base stations.
Present DCA techniques can be grouped into two categories: traffic adaption and interference adaptation. xe2x80x9cTimid,xe2x80x9d xe2x80x9cAggressive,xe2x80x9d and xe2x80x9cm-Persistent Polite Aggressivexe2x80x9d (xe2x80x9cm-PPAxe2x80x9d) systems are examples of interference adaptation techniques. These techniques are also called distributed techniques because they allow mobile units to make decisions concerning channel allocation.
In a xe2x80x9cTimidxe2x80x9d technique a mobile unit measures the interference signal level on a channel pair and seizes that channel pair if the level indicates that no mobile units within a certain area, called a xe2x80x9cneighborhood,xe2x80x9d are using that channel pair. In an xe2x80x9cAggressivexe2x80x9d technique, a mobile unit, after an unsuccessful attempt to find an unused channel pair, sends out a xe2x80x9cseizexe2x80x9d signal on a channel whose interference level indicates that only one other mobile unit in the seizing mobile unit""s neighborhood is using the corresponding channel pair. The other mobile unit, called the disturbed mobile unit, receives the xe2x80x9cseizexe2x80x9d signal and then looks for another channel pair. The xe2x80x9cm-PPAxe2x80x9d technique, is similar to the xe2x80x9cAggressivexe2x80x9d technique, however, if the disturbed mobile unit cannot find another available channel pair the seizing mobile unit releases the seized channel pair and searches for another channel pair.
For xe2x80x9cTimid,xe2x80x9d xe2x80x9cAggressive,xe2x80x9d or xe2x80x9cm-PPAxe2x80x9d techniques to work well, the mobile unit needs to be able to measure all channel pairs to determine which pair to make an attempt on. This may not be feasible. Furthermore, the xe2x80x9cAggressivexe2x80x9d technique can become unstable because when one mobile unit disturbs another it may start a series of changes in channel pair occupancy.
The xe2x80x9cm-PPAxe2x80x9d technique appears to give the best results however this technique also has drawbacks. The delay introduced to see whether a disturbed mobile unit can find another channel pair may not be satisfactory. In addition, multiple attempts to seize channel pairs by multiple mobile units throughout a wireless network may create unsatisfactory levels of interference on many channels.
In traffic adaptation DCA techniques, channel pairs are assigned to or occupied by mobile units based on actual data concerning channel pair usage by mobile units. Traffic adaptation does not require the measuring of interference signal level but rather the reporting of data concerning actual channel pair usage. Maximum Packing DCA (MP DCA) is a theoretical optimum for a traffic adaptation technique. In MP DCA centralized information determines which frequency channel pairs are used by all mobile units in a network. Each time a mobile unit requests a frequency channel pair for communication, the best possible allocation scheme is determined and all channel pair allocations are updated. MP DCA requires centralized coordination and global information, which is almost impossible to achieve in a network with a large number of channels and cells.
One object of the present invention is to provide efficient use of frequency channels in wireless communication systems.
A further object of the invention to provide a dynamic channel allocation technique which does not introduce significant delay in setting up calls or communications between base stations and mobile units.
A further object of the invention is to provide a dynamic channel allocation technique, which produces a minimum amount of interference.
A further object of the invention is to provide an efficient traffic adaptation technique for channel allocation.
The above objects, as well as, other advantages are accomplished in one embodiment of the present invention by providing channel pair occupancy and channel pair availability data at each base station for that base station and for its neighboring base stations. The neighboring base stations can be defined using, for example, a 1-cell or 2-cell buffering reuse constraint. The data is preferably provided in the form of an augmented channel pair occupancy (ACO) table. In this embodiment, the channel pair occupancy and channel pair availability data is used to assign frequency channel pairs to requesting mobile units. Data in the table is changed based on channel pair occupancy and channel pair availability data received from neighboring base stations.
In another embodiment of the invention, dynamic channel allocation is accomplished by providing channel pair occupancy and channel pair availability data at a mobile switching center and using this data to assign channel pairs to requesting base stations and mobile units.
In another form of the present invention, data concerning channel pair occupancy by a base station and channel pairs available to a base station is transmitted from a base station to its neighboring base stations.
In another embodiment, channel pair occupancy and channel pair availability data is provided in the form of multiple tables located at a single mobile switching center and this data is used to assign channel pairs to base stations and mobile units. In another form of the present invention the same data is provided in a combined table located at a single mobile switching center and this data is used to assign channel pairs to base stations and mobile units.